Fix displaying ShowTime applet on all monitors

[dtrunk90]

Fixes #477

Monitors are extending. Proof that the fix works:

[fossfreedom]

Thanks for this - certainly helpful and pin-pointing when the change occurred was very useful.

I think the correct fix is to simply bump the arg used in the window name here: https://github.com/UbuntuBudgie/budgie-extras/blob/f61db0c0deba6812e9a4f3f535c3b5c2bc39a0ce/budgie-showtime/src/showtime_desktop/showtime_desktop.vala#L513

i.e. it should just be changed to:

winname = "Showtime".concat(args[2]);

[dtrunk90]

Indeed it was enough to just have a unique window name.

[fossfreedom]

Much appreciated for helping us through finding and testing this.